The long term objective of this proposal is to understand in molecular terms the mechanism by which Agrobacterium tumefaciens genetically transforms a wide variety of higher plants. Previous studies from the investigator's laboratory have shown that this transformation is the end result of the processing, transfer and integration of a segment (T-DNA) of a large tumor-inducting (Ti) plasmid. These processes are carried out by enzymes coded by a regulon (vir) that is activated by a number of plant signal molecules synthesized by wounded plants in an acidic environment. In this proposal, the investigator has designed experiments to answer the questions of how does the plant recognize the phenolic (AS) plant signal molecules and what domains of the sensor protein interact with AS. This will be achieved by measuring the binding of radioactive AS to purified sensor protein. Alternatively, the investigator will swap domains between different sensor proteins which interact differently with AS. Chromosomal mutants that are avirulent and are unable to induce the vir genes will also be characterized. Understanding the basis for this lack of induction may provide concrete evidence for an undescribed global regulatory system. Additional regulatory mutants which may be involved in vir gene induction will be isolated and characterized. Lastly, using the yeast two hybrid system, the investigator will identify and characterize proteins in yeast, which can also be transformed by Agrobacterium, which interact with the two proteins which associate with the T-DNA.